The formation of oriented barium carbonate from the decomposition of yttria-doped barium zirconate films

Yttria doped barium zirconate (BZY) thin films show promise thanks to their high proton conductivities and their possibility for use in studying fundamental processes such as exsolution. This work demonstrates that highly oriented BZY thin (45 nm) films on (100) single crystal strontium titanate decompose into oriented barium carbonate rods and yttria stabilized zirconia when exposed to industrial grade Ar or pure CO2 at 800 °C. It is shown with transmission electron microscopy that the rods nucleate on the BZY surface. The causes and modes of decomposition in these thin films are discussed in detail.This work was funded through the National Science Foundation via grant DMR1563754. Additionally, this material makes use of the TOF-SIMS system at the Colorado School of Mines, which was supported by the National Science Foundation under Grant No.1726898. JS would like to thank ICN2 for funding through the CERCA program/Generalitat de Catalunya and by the Severo Ochoa program (SEV-2017–0706).Peer reviewe

Point Defects in Magnesium Aluminates Spinel Ceramics Doped with Lithium Fluoride

The nature and topological distribution of optical centers within various regions of hot pressed disks of transparent magnesium aluminates spinel ceramics doped with LiF were studied. In the optical absorption spectra of this type of ceramic, bands were revealed at 4.75 eV and 5.3 eV, which were identified with $F^{+}-$ and F-centers, respectively. Because both bands are formed by anionic vacancies which captured one or two electrons, the topological distribution of anionic vacancies was determined. The band at 5.65 eV was also found which is tentatively identified with complex centers of anionic vacancies that capture fluorine ions and electrons. Using X-ray irradiation the variety of absorption bands of hole centers related to cationic vacancies was established. The spatial distribution of cationic vacancies within the ceramic disk was also determined

Effects of exsolution on the stability and morphology of Ni nanoparticles on BZY thin films

Yttria doped barium zirconate (BZY) is of interest for use as a catalyst support material, supporting exsolved Ni nanoparticles. Exsolution has been hypothesized to impart catalytic nanoparticles with exceptional resistance to particle coarsening, a known degradation mechanism in catalysts. However, the mechanisms and kinetics of Ni nanoparticle coarsening in BZY are unknown. This work analyzes the kinetics of the coarsening of exsolved Ni nanoparticles on epitaxial BZY thin films at three temperatures (600, 700, and 800 C) over a time span of 150 h. It is demonstrated that Ni coarsening transitions from an Ostwald ripening process to particle migration and coalescence after Ni particles reach a critical size. The coarsening behavior of BZY/Ni is shown to be dependent on the BZY surface orientation, with Ni particles on (111) oriented thin films coarsening the least. The preferred orientation relationships between Ni and BZY on (100), (110), and (111) oriented films are determined. Additionally, the morphology of Ni particles produced through exsolution and thin film dewetting are compared, showing that the socketing behavior and interfacial energy are independent of the Ni particle preparation method.The authors would like to thank Dr. Wolfgang Rheinheimer and Dr. Wayne Kaplan for discussions relating to this work. Research funding was provided by the National Science Foundation (DMR1563754). JS would like to thank ICN2 for funding through the CERCA program/Generalitat de Catalunya and by the Severo Ochoa program (SEV-2017-0706). This work makes use of the Tescan S8252 Raman-SEM/FIB at the Colorado School of Mines, funding for which was provided by the National Science Foundation (DMR1828454)